A CAD drawing often begins life as a paper drawing, print, or sketch.
I’m sure you’ve seen this scenario. Your client, boss, or co-worker comes to you with a piece of paper in hand. The paper has information in sketched form which needs to be “cadded.” Or perhaps there is an earlier black and white print of a drawing for which no digital file is available, basically creating a trace-and-redraw job. Or maybe someone has printed something from the Internet and they say, “I want something just like this, except for . . .” 😉
About this time you are thinking,
“How can I quickly turn this analog paper image into a useful, vector-based AutoCAD drawing?”
The first step is getting the information stored on the paper drawing into some digital format that a computer can process, i.e., a raster image file such as a JPEG or TIFF.
Some of us carry a digital camera built right into our smartphone. This makes it a snap to create a JPEG of the paper drawing. Quick and easy.
If you have a scanner available, and if the drawing fits onto the scanner’s panel, you can scan the drawing. By using a scanner, you have the best chance of keeping the proportions of the drawing true. That is, the height and width will stay in a 1:1 ratio with very little distortion or stretching. However many prints are too large to fit on a flat-bed scanner.
I’ve found that the best method, if not always the quickest, is to use a tripod-mounted digital camera. With this method I can count on excellent quality images with minimal distortion.
The increased quality of the images will usually save you time during the CAD part of the project, especially when multiple sheets are involved. My Canon Rebel digital SLR camera is a tool that I absolutely love, and you just can’t beat it for value. Get one along with a tripod and all the goodies by clicking on the link at left.
If you decide to take a photo of the paper drawing using a camera, I think you will get the best results by following these steps:
- Find a place where you can pin or tape the drawing to a flat surface.
- The place you choose should have good light, evenly distributed over the entire surface of the drawing.
- Indirect sunlight from a large window usually works well; you can also use artificial light from two or more evenly distributed sources.
- Mount the camera on a tripod if it’s feasible. A tripod-mounted camera is a big help, especially if you are shooting multiple sheets.
- If you have several drawings to shoot, mark the position of the first drawing on the wall with painters’ tape, for reference in shooting the others.
- Ensure that the lens of the camera is aligned with an imaginary line, exactly perpendicular (90 degrees) to the exact center point of the paper drawing. See diagram at right.
- Place the camera about the same distance away from the paper as the paper’s diagonal width. Too close and you may get wide-angle fisheye-type distortion. Too far away and you risk blurring from camera movement (a tripod eliminates this concern). A telephoto lens produces the most accurate image, if you use a tripod and place the camera carefully.
- If you’re using a smartphone, notice that the camera lens is typically off-center from the body of the phone. Make sure that the lens itself is centered on the paper drawing as shown, and that the imaginary line (yellow in the diagram) is exactly perpendicular to the center point of the sheet.
- You may want to shoot additional close-up, “detail” photos of complex portions of a drawing.
Transferring the Files
After shooting is done, transfer the digital file(s) to your computer by any convenient method, such as a removable memory card, a cable, or by email. Email works best for one or two photos from a smartphone, while a memory card transfer will save time for three or more images.
By the way, I always make sure my CAD computer has an SD memory card reader built in when I’m making a computer purchase, just for this situation.
Please leave your thoughts in the comment box below. Do you have ways that work (or don’t) that you have tried?
In the next post, we will discuss how to turn the JPEG image files into an AutoCAD drawing.
Before I close, I should include this reminder . . .
Always respect other people’s copyrights when using these techniques. It’s good karma, and keeps everyone out of trouble.
Part 2 of the process, inserting the raster image into your AutoCAD drawing, is coming soon in the next post.
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Thanks for reading, and Keep On Cadding! 🙂